When I began my career as a librarian perpetual calendars were published in print almanacs and quick reference books such as The New York Public Library Desk Reference. You can buy a used one for a dollar plus shipping, or a collectible for quite a bit more. With the advent of online "ready reference" this wonderful book has not been published since 2002. Nonetheless, I love it so much that I may ask to have it buried with me! Just kidding, well, maybe not....

Online almanacs and ready reference are the forte of the world wide web. Again, a good basic one, plus a date calculator, lives on Infoplease. It includes the backgrounds of various calendars used worldwide. By the way, 2015 is the Chinese year of the goat.

Ancestor Search on Searching for Your Ancestors has a very useful cast of calendars, including age , day of the week and year calculators.

Keep in mind that most family history programs like FamilySearch and RootsMagic automatically format the correct dates and days when you enter dates. But these are handy when you are investigating rather than recording.